The Influence of Climate on Basaltic Clast Morphometry as an Indicator of Martian Paleoclimate

The martian geologic record provides compelling evidence for an early climate that supported liquid water on or near the surface, yet the environmental conditions during this period remain uncertain. Climate models often support a dominantly icy climate with mean annual temperatures below freezing, while the geomorphological record generally supports non-icy conditions with stable water on the surface. Observations of fluvially-transported rounded clasts by the Curiosity and Perseverance rovers offer new methods into reconstructing past conditions. We use rover-based imagery and visible to near-infrared (VNIR) spectroscopy to quantitatively characterize the transport history of pebble and cobble sized float clasts within the Gale and Jezero fluvial systems on Mars. We have (1) used quantitative field-based relationships between grain shape and transport distance to model the differing climatic effects on clast morphometry; and (2) quantitatively implemented our model to images of rounded clasts on Mars to constrain their transport and climatic history. We find that the analyzed martian clasts fit more closely with our non-icy climate-based transport model based on correlation of modeled transport distances with previously estimated transport distances in Gale crater and compositional comparison with the mineralogy of the catchment of Jezero crater. This indicates that non-icy conditions may have been present on the surface of Mars in these equatorial regions during times of active fluvial activity.